The present invention relates to a pyrotechnic switch for breaking electrical circuits, and to an intermediate circuit discharge system as well as a vehicle having the intermediate circuit discharge system.
Electric or hybrid vehicles have a high-voltage electrical system in which voltages in the range of between 60 V and several hundred volts (for example 400 V) can be applied. The high-voltage electrical system usually includes a high-voltage battery which is coupled to the rest of the high-voltage electrical system via a so-called intermediate circuit which contains at least one intermediate circuit capacitor. In the event of an electric or hybrid vehicle being involved in an accident, the high-voltage electrical system can present a potential hazard for occupants of the vehicle, other road users or emergency service personnel.
Therefore, it has to be possible to reliably disconnect the high-voltage electrical system, that is to say the high-voltage battery has to be reliably decoupled from the high-voltage electrical system, in the event of an accident.
Emergency switches serve to break electrical circuits in an emergency, in particular to disconnect electrical energy sources from connected electrical systems, said emergency switches being tripped and interrupting the electrical circuit as necessary. Emergency switches of this kind have to safely interrupt the electrical circuit without permitting unintended reconnection. In the event of an accident, the high-voltage battery of the electric vehicle has to be disconnected from the rest of the on-board electrical system in order to prevent a fire from starting.
After the high-voltage battery is disconnected from the high-voltage electrical system of an electric or hybrid vehicle, a considerable quantity of energy can still be stored in one or more intermediate circuit capacitors. For safety reasons, the high-voltage intermediate circuit, in particular the intermediate circuit capacitor or capacitors arranged therein, should therefore be discharged as quickly as possible to a relatively safe voltage level of, for example, less than 60 V (within a time period of, for example, less than 5 seconds).
The discharging of the high-voltage intermediate circuit can be controlled via the power electronics system. A discharge circuit can be provided for this purpose. The discharge period can be controlled via a switch in connection with a non-reactive resistor. Since the energy of high-voltage intermediate circuits can be discharged only slowly in the seconds range, for example 5-40 seconds, according to the current prior art, the energy could also lead to a safety risk.
As illustrated in FIG. 1 (prior art), the high-voltage components are provided with a passive and an active discharge branch in the intermediate circuit in the case of conventional electric vehicles. The passive discharging serves to discharge the intermediate circuit. The active discharging is switched on when a changeover is made to the inoperative state or in the event of a fault, for example crash, in order to reduce the available energy in the intermediate circuit. In the case of the current prior art, energy is reduced in the seconds range (for example 5-40 seconds). The longer the discharge process in the intermediate circuit, the greater the safety risk.
The requirements made of future high-voltage systems have considerably increased, that is to say the discharge periods have to be comparatively short. To date, there has been no satisfactory concept in respect of how the electrical energy stored in the intermediate circuit capacitors can be reliably reduced in a short time (for example 10-30 milliseconds) in emergency situations without large and expensive components which take up installation space.
Pyrotechnic switches, which are also called pyrotechnic fuses, serve to interrupt an electrical circuit in a targeted and safe manner when certain conditions occur. Pyrotechnic switches have a rapid disconnection response, this allowing the high-voltage battery to be safely disconnected from the high-voltage electrical system of a vehicle within an extremely short time after said vehicle is involved in a crash. Reference may be made, by way of example, to DE 102 09 627 A1 which discloses a pyrotechnic switch for disconnection purposes, which pyrotechnic switch has a body in which two conductor regions and a predetermined disconnection point, which is arranged between said conductor regions, are provided. A cavity in the body surrounds an ignition device. After the ignition device is tripped, the predetermined disconnection point is broken down into small pieces and therefore the two conductor regions are disconnected from one another. A pyrotechnic switch of this kind can serve only to break an electrical circuit.
The object of the present invention is to provide a pyrotechnic switch which is suitable for reliably disconnecting a high-voltage battery of an electric or hybrid vehicle from the high-voltage on-board electrical system and which furthermore still has an additional functionality. A further object of the invention is to provide an intermediate circuit discharge system comprising a pyrotechnic switch of this kind.
The pyrotechnic switch according to the invention comprises a first electrical conductor, a second electrical conductor, and an ignition element. In a first state of the pyrotechnic switch, the first electrical conductor and the second electrical conductor are electrically connected to one another. A predetermined disconnection point is provided between the first and the second electrical conductor. The predetermined disconnection point is disconnected, that is to say the first electrical conductor is isolated from the second electrical conductor, as soon as the ignition element is tripped. Therefore, the ignition or tripping of the ignition element causes disconnection of the predetermined disconnection point and therefore an interruption in the previously existing electrical connection between the first and the second electrical conductor.
The pyrotechnic switch according to the invention has a third electrical conductor. In the first state of the pyrotechnic switch, the third electrical conductor is electrically isolated from the first electrical conductor and from the second electrical conductor. In a second state of the pyrotechnic switch according to the invention, that is to say after the ignition element is tripped or ignited, the third electrical conductor is electrically connected to the second electrical conductor. However, in the second state, the third electrical conductor is still electrically isolated from the first electrical conductor.
A pyrotechnic switch of this kind can be used, in its first state, as an “electrical connection” between a high-voltage battery and a high-voltage on-board electrical system of a vehicle. Owing to the ignition of the ignition element, the pyrotechnic switch according to the invention moves to its second state in which the second and the third electrical conductor are connected to one another, and this can be used for the targeted discharging of capacitors, that is to say for the targeted reduction in electrical voltages (for example in an intermediate circuit of the high-voltage on-board electrical system).
The pyrotechnic switch preferably has a housing with a cavity in which the ignition element is arranged.
The ignition element can generate an increase in pressure in order to sever the predetermined disconnection point as soon as the ignition element is tripped.
In the second state of the pyrotechnic switch, the second electrical conductor and the third electrical conductor are connected to one another in such a way that the second electrical conductor is pushed against the third electrical conductor after the predetermined disconnection point is severed or vice versa, that is to say the third electrical conductor is pushed against the second electrical conductor after the predetermined disconnection point is severed. The tripping of the ignition element therefore causes a mechanical movement of the second or third electrical conductor relative to the other, so that the second and the third electrical conductor contact and are electrically connected to one another.
In the second state of the pyrotechnic switch, the first electrical conductor is preferably isolated not only from the second electrical conductor but rather also furthermore from the third electrical conductor.
The pyrotechnic switch can preferably have a disconnection bolt which can be electrically insulating when, in the second state of the pyrotechnic switch, the second and the third electrical conductor are directly electrically connected to one another.
An end face of the disconnection bolt preferably has a tapering, for example conical, portion, wherein the disconnection bolt disconnects the predetermined disconnection point in such a way that, after the ignition element is tripped, the tip of the conical portion pushes the second electrical conductor away from the first electrical conductor and interrupts the predetermined disconnection point.
In one variant of the invention, the ignition element is arranged in the first electrical conductor or integrated into the first electrical conductor. When the ignition element is tripped, the predetermined disconnection point is disconnected and the second electrical conductor is pushed away from the first electrical conductor, as a result of which the electrical connection between the first and the second electrical conductor is interrupted.
In a further variant of the invention, the pyrotechnic switch comprises a viscous material which serves to sever the predetermined disconnection point. After the ignition element is tripped, the viscous material pushes the second electrical conductor away from the first electrical conductor and interrupts the predetermined disconnection point.
The invention furthermore proposes an intermediate circuit discharge system in which the abovementioned pyrotechnic switch is used.
The intermediate circuit discharge system according to the invention, in particular for an electric or hybrid vehicle, has the above-described pyrotechnic switch and an intermediate circuit of a high-voltage electrical system of the vehicle, wherein the intermediate circuit has an intermediate circuit capacitor. The first electrical conductor of the pyrotechnic switch is connected to a high-voltage battery. The second electrical conductor of the pyrotechnic switch is connected to a first connection of the intermediate circuit capacitor, and the third electrical conductor of the pyrotechnic switch is connected to a second connection of the intermediate circuit capacitor.
In the first state of the pyrotechnic switch, the pyrotechnic switch connects a high-voltage battery to the intermediate circuit of the high-voltage electrical system of the electric or hybrid vehicle via the first and the second electrical conductor. In the second state of the pyrotechnic switch, the pyrotechnic switch connects the first connection of the intermediate circuit capacitor to the second connection of the intermediate circuit capacitor, as a result of which a discharge circuit is closed, the intermediate circuit capacitor being discharged via said discharge circuit. The intermediate circuit discharge system preferably has a discharge resistor, wherein the third electrical conductor of the pyrotechnic switch is connected to the second connection of the intermediate circuit capacitor via the discharge resistor. The discharge circuit is preferably dimensioned such that the voltage across the intermediate circuit capacitor is reduced to a voltage of less than 60 volts in a time period of less than 100 milliseconds.
The pyrotechnic switch can preferably be tripped by a tripping signal of the electric vehicle. The tripping signal may be, for example, a crash signal which is generated by a crash sensor and indicates that the electric or hybrid vehicle is or has been involved in a crash in which a predefined threshold for a degree of deformation and/or a predefined acceleration value have been exceeded.
The intermediate circuit capacitor preferably has a value of from 0.5 mF up to 4 mF. If this value is less than 4 mF, the capacitor is relatively cost-effective. If this value is greater than 0.5 mF, a few high-frequency ripples are produced, and this can have an adverse effect on the electromagnetic compatibility (EMC).
The discharge resistor preferably has a value of from 0.2 ohm up to 10 ohms. If this value is greater than 15 ohms, the discharge period is comparatively long. If this value is less than 0.1 ohm, the flowing current is comparatively large.
The present invention furthermore also proposes an electric vehicle or a hybrid vehicle comprising an abovementioned intermediate circuit discharge system.
According to the invention, a high-voltage battery can be disconnected from the on-board vehicle electrical system in the millisecond range after the tripping operation. The discharge circuit is connected by way of the pyrotechnic switch establishing a new electrical connection, that is to say a connection of the second and the third electrical conductor, after the tripping operation. The energy which is stored in the intermediate circuit can be reduced completely or at least to an extent such that danger to emergency service personnel is precluded, by means of the intermediate circuit discharge system comprising the pyrotechnic switch according to the invention, within a very short time period (for example 1-10 milliseconds after the pyrotechnic switch is tripped).
Owing to the invention, the time which is required for discharging the intermediate circuit can be reduced by a factor of 1000 (milliseconds instead of seconds) in comparison to the prior art, without increasing the costs and the installation space for the discharge circuit.
The basis of the invention is the use of a pyrotechnic switch as a disconnection element in the high-voltage storage device. The pyrotechnic switch can both safely disconnect the high-voltage battery from the rest of the high-voltage on-board electrical system and also establish a new connection after the pyrotechnic switch is tripped, so that a discharge circuit can be formed, said discharge circuit discharging the energy which is stored in the intermediate circuit capacitors of the high-voltage components.
High currents can be transmitted by the comparatively solid contacts (first, second electrical conductors) of the pyrotechnic switch, which high currents allow discharge of the intermediate circuit in the millisecond range. Owing to the irreversible nature of the process, the connection between the high-voltage storage device and the high-voltage components cannot be unintentionally re-established. The contact which is closed during the tripping of the pyrotechnic switch is closed only one single time. Therefore, the reliability is also certainly ensured. Special coatings which are necessary for electromechanical switches which open/close several times are not required.
The electromechanical switch shown in FIG. 1 (prior art) can be replaced by a pyrotechnic switch according to the invention. In addition, a pyrotechnic switch is more cost-effective than an electromechanical switch. The pyrotechnic switch according to the invention allows more rapid discharging of the intermediate circuit and constitutes a cost-effective, reliable and installation space-saving solution.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.